A known plate making process for electrophotographic plate making materials, comprises uniformly electrically charging the electrophotographic plate making material by corona discharge, imagewise exposing it to light, forming a toner image by liquid toner development, fixing the toner image by heating, and changing the nonimage part so as to have a hydrophilic property by processing with a desensitizing solution (etching solution) to obtain a printing plate.
Hitherto, such a plate making process has been carried out using a plate making machine, for example, shown in FIG. 1. Namely, in the prior plate making machine 1, as shown in FIG. 1, an electrophotographic plate making material 13 held in a preset part 2 in the form of a roll or sheet is guided by sending rolls 14 and 15 into an electric charge part 3 and uniformly electrically charged by corona discharge. It is then guided by a press roll 21 and a sending belt 20 into an exposure part 4 and imagewise exposed to an original 8 through a projection optical system 9 comprising a light source 11 and a reflection mirror 10. The imagewise exposed plate making material is then sent to a liquid toner development part 5 by rolls 16 and developed with a toner supplied from a liquid toner tank 12. It is then sent to a fixation part 6 by rollers 17 and 18. After being fixed by heating, it is collected as a printing plate in a collection part 7 by rolls 19.
In the plate making process, a step for fixing by heating after liquid toner development is particularly important for obtaining excellent properties, which is different from the image recording process by electrophotography. Namely, in order to obtain a printing plate having excellent images and sufficient printing durability, it is necessary to carry out fixation at a suitable temperature for a suitable time so as to fit properties of the toner. If the fixation is carried out rapidly at a too high temperature, the line image becomes blurred or resolving power deteriorates. If the fixation is carried out unevenly at a too low temperature, the press life remarkably reduces.
In a liquid toner developer, generally, a polymer or resin having electric charges is dispersed as fine particles having a size of about 0.01.mu. to 10.mu. in an electrically insulating liquid such as liquid hydrocarbons or halogenated hydrocarbons, for example, a petroleum solvent. Another problem in the step for fixing by heating is that the heating is carried out in the presence of an inflammable gas of the petroleum solvent carried therein.
The function of the fixation part of the conventional plate making machine is to complete the drying of the toner solvent adhered to the plate making material by evaporation and thermal fusion of components of toner particles within a short time of, generally, several seconds or less. It is effective to use a method of blowing hot air against the surface of the passing plate making material by means of an electric heater and a fan. However, if plate making is continuously carried out for a long time, evaporation of the solvent continues to increase a gas concentration of the solvent in the atmosphere, and there is thus the possibility of ignition or explosion due to a heater. In order to prevent such a danger, it is possible to use a plate heater. In this process, a panel heater controlled so as to have a fixed temperature in a range from about 80.degree. to 150.degree. C. is placed in the fixation part and the fixation is carried out by bringing the back of the plate making material into contact with the panel heater. According to this process, the danger of ignition or explosion diminishes even if the gas concentration of the solvent increases. However, this process is not desirable because the fixation requires too much time because fixing ability is inferior as compared with the above described process which comprises drying with hot air by heating.
As an electrophotographic plate making material capable of use for the present invention, there is, for example, an electrophotographic plate making material which has a base having a laminated layer composed of polyolefin or metal foil on at least one side of the paper stock and having a volume resistance of 10.sup.10 .OMEGA. or less and a photoconductive layer provided on said base. The volume resistance is obtained by reading a value of electric current (A) upon an application of direct current voltage (V) when a sample is interposed by two disc electrodes made of metal having 2.5 cm of raius.
Volume resistance R.sub.V =V/A(.OMEGA.) However, when this material is rapidly heated to 80.degree. to 100.degree. C. or more by bringing it into direct contact with the fixation part, the laminated layer becomes soft or the surface friction resistance becomes high to make it difficult to pass the laminated material through the fixation part, i.e., to deteriorate passing behaivor.